Apparatus and method for detecting venous needle dislodgement

ABSTRACT

Apparatus that detect an interruption of the connection between a blood treatment apparatus and a patient blood circulation which can be connected to the blood treatment apparatus via a connection means is described. The connection means can be attached to a fluid line. The apparatus includes a line shut-off and a pressure sensor which is configured to measure the fluid pressure prevailing in the fluid line at a position located between the line shut-off and the connection means. A control and evaluation unit is configured to evaluate the pressure or pressure curve occurring after blocking the line so as to detect an interruption or disturbance of the connection between the connection means and the patient blood circulation.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to German application DE 10 2014 102731.0 filed Feb. 28, 2014, the contents of such application beingincorporated by reference herein.

FIELD OF THE INVENTION

The invention relates to an apparatus and a method for detecting venousneedle dislodgement as well as an apparatus for extracorporeal bloodtreatment equipped with the same. The apparatus for extracorporeal bloodtreatment can be configured for carrying out a blood treatment therapysuch as hemodialysis, hemofiltration or hemodiafiltration. In this casepreferably an apparatus for monitoring a vascular access duringextracorporeal blood treatment is used.

BACKGROUND

For blood treatment the blood of a patient can be guided via anextracorporeal blood circulation, for example in the course ofhemodialysis, hemofiltration or hemodiafiltration. In order to obtainaccess to the patient's vascular system arteriovenous fistulae, shuntsor else vascular implantations can be used. The connection of theextracorporeal blood circulation to the patient is usually made viacatheters or cannulas or, respectively, needles, e.g. dialysis cannulasor needles, by which a fistula or a shunt or, respectively, a vascularimplantation, for example, is punctured and fluid communication isestablished in this way.

At the beginning of or else during blood treatment the case may occurthat the venous access to the blood circulation is disturbed, if, forexample, the needle or cannula gets out of place and the extracorporealcirculation is no longer connected properly, or is no longer connectedat all, to the intracorporeal blood circulation, i.e. the patient'sblood circulation. This may cause problems especially in the case ofdislodgement of the venous access to the patient's blood circulation.Unless such dislodgement of the venous access is detected in due time,blood continues being withdrawn from the patient via the arterial accessbut is no longer properly returned into the patient's body after theextracorporeal blood treatment. In the case of common blood flow ratesof 300 to 400 ml/min, for example, a critical situation will developwithin a few minutes.

DESCRIPTION OF THE RELATED ART

EP 1 584 339 B1 discloses a method for detecting needle dislodgementbased on the measurement of arterial and venous pressures while sums anddifferences are formed.

In an apparatus according to U.S. Pat. No. 7,648,474 B2 the arterial andvenous pressure values are monitored for determining needledislodgement.

SUMMARY OF THE INVENTION

Aspects of the invention provide an apparatus according to claim 15 anda method according to claim 23.

By the apparatus according to aspects of the invention and the methodaccording to aspects of the invention for example venous needledislodgement can be detected at an early stage and in this way highpatient safety during a treatment such as a dialysis treatment as wellas high functional reliability of the apparatus according to aspects ofthe invention can be ensured.

Further developments of aspects of the invention are defined in thedependent claims.

Embodiments of the apparatus according to aspects of the invention servefor detecting an interruption of the connection between a bloodtreatment apparatus and a patient blood circulation which can beconnected to the blood treatment apparatus via a connection means, forexample a needle. The connection means, for example the needle, can beattached to a fluid line, optionally to the end thereof. One or moreembodiments of the apparatus according to aspects of the inventioninclude a line shut-off, a pressure sensor configured to measure thefluid pressure prevailing in the fluid line at a position locatedbetween the line shut-off and the connection means and a control andevaluation unit configured to evaluate the pressure or pressure curveoccurring after blocking the line so as to detect herefrom aninterruption or disturbance of the connection between the connectionmeans and the patient blood circulation. An interruption or disturbanceof the connection is also referred to as needle dislodgement in theforegoing and hereinafter.

The apparatus can be part of a blood treatment apparatus, for example adialysis apparatus. A display and/or alarm device can be provided forgenerating a display or an alarm in the case of detection of aninterruption or disturbance of the connection.

The apparatus may be configured to compare the pressure occurring in thefluid line and being measured continuously or repeatedly after closingthe line shut-off to a threshold and/or to determine the rate of thepressure drop and/or to determine a final pressure value which tends tobe resulting and/or to detect whether the pressure tends towardatmospheric pressure or a higher pressure occurring in the patient bloodcirculation.

The apparatus may include a blood pump which continues to be operableeven after actuation of the line shut-off with corresponding fluidblocking of the fluid flow through the line shut-off, wherein the pumpedfluid can be intermediately stored in a collecting means, for example abubble collector.

The apparatus may be configured to stop the operation of the blood pump,when a collecting means receiving the pumped fluid is filled with theline shut-off being closed and/or when dislodgement of the connectionmeans is determined and/or when a fluid pressure measured by thepressure sensor reaches or falls below a particular limit.

By aspects of the invention also a method for detecting an interruptionof the connection between a blood treatment apparatus and a patientcirculation is provided which can be connected to the blood treatmentapparatus via a connection means, e.g. a needle. The connection means,e.g. the needle, can be attached to a fluid line, optionally to the endthereof. In one or more of the embodiments of the method the fluidpressure prevailing in the fluid line is measured via a pressure sensorat regular or irregular time intervals at a position located between aline shut-off and the connection means, wherein the fluid line isblocked at regular or irregular time intervals and the pressure orpressure curve occurring in the fluid line after blocking the fluid lineis evaluated so as to detect herefrom an interruption or disturbance ofthe connection between the connection means and the patient bloodcirculation.

If an interruption of the connection is detected, a display or an alarmcan be generated.

The pressure occurring in the fluid line and being measured continuouslyor repeatedly after closing the line shut-off can be compared to athreshold and/or the rate of the pressure drop can be determined and/ora final pressure value to be expected can be determined and/or it can bedetected whether the pressure tends toward atmospheric pressure or ahigher pressure occurring in the patient blood pressure.

A blood pump may continue to operate even after actuating the lineshut-off with corresponding fluid blocking of the fluid flow through theline shut-off, wherein the pumped fluid is intermediately stored in acollecting means, for example a bubble collector.

The operation of a blood pump can be stopped, when a collectingcontainer receiving the pumped fluid is filled with the line shut-offbeing closed and/or when dislodgement of the connection means isdetermined and/or when a fluid pressure measured by the pressure sensorreaches or falls below a particular limit.

The line shut-off can be re-opened as soon as it is detected that nointerruption or disturbance of the connection is provided between theblood treatment apparatus and the connection means.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is best understood from the following detailed descriptionwhen read in connection with the accompanying drawings. Included in thedrawings are the following figures:

FIG. 1 shows an embodiment of an apparatus according to aspects of theinvention;

FIG. 2 shows a pressure curve before and after needle dislodgement;

FIG. 3 shows an embodiment of a method for detecting needledislodgement;

FIG. 4 shows a diagram of the pressure curve in time in the case ofneedle dislodgement and a subsequent check of dislodgement;

FIG. 5 shows an example of a pressure curve as well as of the timesequence of the method steps of an embodiment of the method according toaspects of the invention;

FIG. 6 shows in two series of curves pressure curves in time before,during and after a fluid flow shut-off;

FIG. 7 illustrates two examples of the pressure curves in the case ofproper needle connection or in the case of needle dislodgement; and

FIG. 8 shows two exemplary pressure curves in their time progression inthe case of connection or dislodgement.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

It is possible by embodiments of the apparatus according to aspects ofthe invention and of the method according to aspects of the invention todetect venous needle dislodgements (VND), as they are called. Forexample, due to movements of the patient or insufficient fastening ofthe needle, the needle can get out of place or even completely slip outof the puncture site. This is problematic especially in the area of thevenous needle, as the blood is returned to the patient via said needle,the blood being correspondingly pressurized in this case. This can evenfurther increase the risk of undesired dislodgement up to slip-out ofthe needle.

In the present context, by the term needle dislodgement both completeslipping of the needle out of the venous vascular access and onlypartial dislodging of the needle with a restricted connection which isstill existing to a certain extent, however, to the blood circulation isunderstood. When the needle gets out of place only partially, the needlecan be located in the tissue surrounding the actual access site andcause perivascular hemorrhage there.

For detecting venous needle dislodgement in general the venous pressurecan be monitored. However, mainly in the case of smaller cannulacross-sections the pressure drop at the cannula may be rather high sothat no significant pressure drop is evident, even if venous needledislodgement has taken place. Also hydrostatic pressure variations canimpede or rule out the detection of pressure variations due todislodgement.

In embodiments of the apparatus according to aspects of the inventionand the method according to aspects of the invention it is provided tostop or at least restrict the fluid flow, i.e. the blood flow, before orduring pressure measurement or pressure monitoring is carried out. Inthis way the afore-mentioned problem of high flow resistance in thecannula with the related offset in the measuring signal can at least bereduced.

Hereinafter blood guiding, e.g. a system or an arrangement in whichfluid, e.g. blood, withdrawn from an object or a patient is guidedoutside the patient blood circulation in the extracorporeal circulationand is subsequently supplied to the patient blood circulation again, isreferred to as extracorporeal circulation. The venous branch of theextracorporeal circulation may comprise, for example, a tube returningthe fluid from the treatment apparatus to the object or patient, namely,discharging the fluid, which can also be in the form of a blooddischarge line of the dialyser.

Embodiments of the invention do not only allow detecting an insufficientconnection of a cannula such as a venous cannula up to the slip-out ofthe cannula from the access site provided, but also detecting a bloodleakage in the venous branch downstream of the apparatus for detectingan interruption of connection. This may be realized, for example, in adouble-needle operation of the blood treatment machine such as thedialysis machine.

FIG. 1 shows an embodiment of a dialysis apparatus according to aspectsof the invention as well as an embodiment of an apparatus according toaspects of the invention for detecting venous needle dislodgement aswell as a configuration of a method according to aspects of theinvention for detecting such venous needle dislodgement in an embodimentof a dialysis method according to aspects of the invention.

FIG. 1 illustrates an embodiment of a dialysis apparatus equipped withan embodiment of a system for detecting venous needle dislodgement. Theembodiment shown in FIG. 1 of the apparatus according to aspects of theinvention for detecting a faulty or missing connection of a venouscommunication between the extracorporeal blood circulation and thepatient blood circulation is illustrated by way of a dialysis machine.Instead of or in addition to hemodialysis also pure hemofiltration orhemodiafiltration can be realized.

The embodiment according to FIG. 1 comprises a dialyser 1 divided by asemipermeable membrane into a first chamber 29 arranged in a dialysisfluid path and a second chamber 30 which in turn is connected to thedialyser inlet with a blood supply line 32 leading away from the patientblood circulation. Via a dialysis outlet including a blood dischargeline 31 leading to the patient the second chamber 30 is connectable tothe blood circulation of the patient so as to supply the purified bloodto the latter again. The first chamber 29 is connected to an intake 20for fresh dialysis fluid and a drain 10 for used dialysis fluid.

Via a pressure sensor 41 the venous pressure can be detected afterclamping off a tube shut-off (tube shut-off clamp or tube clamp) 40and/or after stopping a blood pump 34. The tube clamp 40 can be operatedmanually or automatically and can cause complete or only partialshut-off of the fluid flow circuit back to the venous access of thepatient. In the embodiment according to FIG. 1 the additional pressuresensor 41 for the venous pressure is disposed between the tube clamp 40and the venous patient access and consequently is located in the bloodreturn line to the patient. Since the pressure sensor 41 is arranged atthe blood discharge line 31 directly ahead of the patient or in any casedownstream of the tube clamp 40, the pressure from the patient access isadjusted at the pressure sensor 41 in the case of proper connection tothe patient circulation, whereas the atmospheric pressure is measured,if the needle has slipped completely or partly out of the patientaccess.

The embodiment includes the pressure sensor 41 in the tube (blooddischarge line) 31 supplying blood to a venous needle 31 a, which tubeis arranged downstream of the tube shut-off or tube clamp 40 andupstream of the needle 31 a, i.e. at the line portion between the tubeshut-off 40 and the needle 31 a. As illustrated in FIG. 1, in thearterial branch 32 of the extracorporeal blood circulation, i.e. in thecirculation leading from the patient to the dialyser inlet, there isarranged a pressure sensor 33 at the blood supply line 32 leading fromthe patient to the dialyser inlet and a bubble collector 35 betweenwhich the blood pump 34 is inserted in the blood supply line 32. Anotherpressure sensor 36 detects the pressure of the blood directly at thedialyser inlet of the dialyser 1. The dialysis fluid is guided in thedirection symbolized by the arrows via the dialysis fluid supply line 20to a first chamber 29 of the dialyser 1 and from there is guided via thedialysis fluid discharge line 10 to the drain or waste. The blood to bepurified flows through the second chamber 30 of the dialyser 1 and isguided at the dialyser outlet in the arrow direction to the blooddischarge line 31.

In the blood discharge line 31 another bubble collector 38 is optionallyprovided. A pressure sensor 37 detects the pressure in the blooddischarge line 31 at the outlet of the dialyser 1.

The flow shut-off 40, which may also be in the form of a tube shut-offor a tube shut-off clamp, is provided, viewed in the blood flowdirection, upstream of the pressure sensor 41 arranged at or in theblood discharge line 31. The blood supply line 32 and the blooddischarge line 31 can be tubes, for example.

In the embodiment the blood of a patient is guided in an extracorporealcirculation and flows through the tube 32 into the blood-side chamber 30of the dialyser 1, whereupon the purified blood is returned to thepatient through the blood discharge line 31.

The flow rate of the blood circulation (extracorporeal) is controlled bythe blood pump 34, wherein at or in the tube 32 the pressure sensor unit33 for arterial pressure measurement is disposed upstream (viewed in theflow direction).

The bubble collector 35 serves for collecting the air bubbles in thearterial tube segment, wherein a further pressure sensor unit 36 isprovided between the bubble collector 35 and the dialyser 1.

In the shown embodiment, the pressure sensor 41 is arranged between thetube shut-off 40 and the patient at or in the blood discharge line 31.

The dialysis fluid of the dialysis fluid chamber 29 of the dialyser issupplied via the dialysis fluid supply line 20, the dialysis fluidchamber 29 being separated from the blood chamber 30 by a semipermeablemembrane. The dialysis fluid is provided by a fluid source (not shown),flows through the tube 20 and is pumped through a pump (not shown) intothe chamber 29 of the dialyser, flows through the same and issubsequently supplied to a waste container via the tubing system 10.

In the blood supplying tube (blood supply line) 31 downstream of thedialyser 1 the pressure sensor 37 for venous pressure measurement isarranged followed by the bubble collector 38. In the flow direction thetube shut-off 40, for instance in the form of a tube shut-off clamp,follows hereto so as to disconnect the patient on the venous side, forexample in the case of fault or for specifically carrying out detectionof needle dislodgement.

If the blood pump 34 is not stopped during measurement for venous needledislodgement, preferably in the line area between the blood pump 34 andthe tube shut-off 40 optionally a reservoir for receiving the pumpedblood is provided. The pumped blood can also be received, for example,by the bubble collectors 35 and/or 38.

After measurement for possible needle dislodgement the bloodintermediately stored in the bubble collector 38 and/or 35 can be slowlyreturned to the patient again after opening the tube shut-off 40 so thatthe storage volume of the bubble collectors 38 and/or 35 is availableagain for receiving blood during a subsequent measurement.

In one or more embodiments a level regulation in the storage volumes ofthe bubble collectors 35 and/or 38 is provided in this respect so thatthe level of the fluid quantity stored in the bubble collectors 35and/or 38 is regulated to a desired level when the tube shut-off 40 isopened.

A control means, e.g. in the form of a data processing and storage unit50, controls all elements shown in FIG. 1 via appropriate interfaces,wherein FIG. 1 only illustrates the connection to the pressure sensor 41and the tube shut-off 40. The data processing and storage unit 50 alsocollects information about other parameters of the dialysis apparatus,e.g. blood flow, dialysis fluid flow and/or treatment period. Theseparameters are processed along with the measured data. The dataprocessing and storage unit 50 serves for processing the measuredpressure values as well as for controlling the blood shut-off and themeasuring times. Furthermore, an internal or external storage unit maybe present for storing the measuring values as well as the controltimes.

The measuring values of the pressure sensors 33, 36, 37 and 41 aretransmitted via data communications, which may be cable-bound and/orwireless, to the data processing and storage unit 50 which is in theform of a data processing and evaluation unit so as to identify venousneedle dislodgements.

The embodiment of the dialysis machine according to aspects of theinvention or the apparatus according to aspects of the invention fordetecting needle dislodgement moreover includes an output unit 51 in theform of a warning signal unit or display which is connected to the dataprocessing and storage unit 50 via a cable-bound or wireless datacommunication. The output unit 51 outputs an optical and/or acousticwarning signal and/or a text for explaining a problem on a display, forinstance, if malfunction of the dialysis machine and/or the apparatusfor detecting needle dislodgement and/or venous needle dislodgementis/are detected. Moreover, the output unit 51 can be configured foroptical, acoustic or electronic output or an output in any other form,for example in the form of electronic storage, printout, e-mailtransmission or the like.

The embodiment according to FIG. 1 may furthermore comprise additionalmeasuring means, pumps, bubble collectors etc. which are not shown.

It may be provided in embodiments to simply stop or restrict the bloodpump 34 so as to inhibit or to reduce the blood flow. Preferablyalternatively or additionally, however, the tubing system guiding thepurified blood to be supplied is also (completely or partly)disconnected ahead of the measuring device for the detection of, e.g.venous, needle dislodgement.

FIG. 2 illustrates an example of a pressure curve at the pressure sensor37 for venous pressure measurement before and after venous needledislodgement, i.e. an undesired partial or complete separation of theconnection between the dialysis apparatus and the patient bloodcirculation. The upper curve 2 a symbolizes the venous pressure curveadjusted in the blood discharge line 31, while the lower steady curve 2b indicates the venous blood pressure in the access and thus in the bodyof the patient subjected to dialysis or to a blood treatment. Thewaveform of the upper pressure curve 2 a is generated by the blood pump34. The lower curve 2 b constitutes the shunt or intravascular pressureand shows the pulsation modulated by the patient's heartbeat. The timeof undesired needle dislodgement is shown by a vertical line. As isevident, after that the venous pressure curve decreases by about 20 to40 mmHg. It is visible from FIG. 2 that the pressure drop after venousneedle dislodgement at the pressure sensor 37 for venous pressuremeasurement is relatively small and merely amounts to about 20 to 40mmHg. The pressure drop thus is within an order of magnitude which canalso be caused by other reasons such as movements of the patient orlowering of the patient's table. Thus this decrease is rather difficultto detect in a reliable manner.

In embodiments of the invention the distinction of the reason for thechange of pressure is considerably simplified, as the pressure pulsesgenerated by the extracorporeal blood pump 34 are no longer included inthe measuring signal, when the extracorporeal blood pump 34 is switchedoff or at least the blood flow is inhibited or at least restricted.Otherwise the pressure pulses are equally within the order of thepressure changes.

By embodiments of the apparatus according to aspects of the invention,which can also be referred to as system according to aspects of theinvention, venous needle dislodgements can be detected easily, reliablyand quickly.

In the embodiment of the apparatus according to aspects of the inventionin accordance with FIG. 1, the air bubble collector 35 and/or 38moreover serve as storage volumes, where appropriate, so that the bloodpump 34 can continue running even when the clamp 40 is closed.Alternatively or additionally the blood pump 34 can also be switched offor continued to be operated to a reduced degree as regards its pumpingrate when the clamp 40 is closed. In the embodiment the pressure ismeasured by the pressure sensor 41 with a stopped blood flow or with ablood flow at least reduced in a defined manner. In this embodiment ofthe apparatus according to aspects of the invention, the blood pump 34can continue pumping even during and after closing the clamp 40 fordetecting needle dislodgement and the course of the treatment is notimpaired by the measurement at least on the arterial side.

The extracorporeal blood circulation can be monitored for detectingvenous needle dislodgement in blood treatment apparatuses working insingle-needle operation as well as in blood treatment apparatusesworking in dual-needle operation including an arterial cannula and avenous cannula for producing the patient's access.

Thus the invention provides an apparatus and a method for detectingneedle dislodgement at the vascular access, e.g. the venous vascularaccess. This apparatus and this method can be used, for instance, in anapparatus and a method for extracorporeal blood treatment, especially achronical blood purification therapy such as hemodialysis,hemofiltration and hemodiafiltration. Thus the vascular access can bemonitored during the extracorporeal blood treatment and both needledislodgement and needle displacement at the venous vascular access canbe safely identified. Even a blood leakage, e.g. in the venous branch,in the flow direction behind the clamp 40, of the extracorporealcirculation can be reliably detected.

The return of the purified blood leaving the dialyser 1 to the patientcan be blocked or at least restricted by the tube shut-off 40.

Viewed in the direction of blood flow, in an embodiment the tubeshut-off 40 may form the last but one component and the pressure sensor41 may constitute the last component of the apparatus for extracorporealblood treatment. The tube shut-off 40 the flow from the pressure sensor41 to the return into the patient to be stopped or at least restrictedby actuating the tube shut-off 40.

The pressure sensor 41 need not necessarily be the last component beforethe return of the blood to the patient. It is preferred, however, thatbetween the pressure sensor 41 and the inlet site of the purified bloodinto the patient circulation no further components are provided whichdefinitely influence the time progression of the pressure measured bythe pressure sensor 41 during measurement, when the tube shut-off 40,e.g. tube shut-off clamp, is closed, in a significant or non-predictablemanner. In one, more or all embodiments the tube shut-off 40 is providedahead of the pressure sensor 41, viewed in the direction of blood flow.In one, more or all embodiments, viewed in the direction of blood flow,initially all other components, especially those which are capable ofinfluencing the pressure such as bubble collectors, pressure sensors,measuring means etc. are provided starting from the dialyser 1 along theblood discharge line 31, wherein the tube shut-off 40 is positioned asthe last but one of these components and the pressure sensor 41 isarranged in these or other embodiments as the last component of theembodiment of the apparatus of the invention, which is only followed,viewed in the direction of blood flow, by the needle leading into thepatient the proper positioning and fluid connection of which is to bedetected (dislodgement).

The tube shut-off 40 and the pressure sensor 41 are connected to thecontrol means 50 which transmits instructions for blocking and releasingthe fluid flow to the tube shut-off 40 and measures the pressuremeasured by the pressure sensor 41 after shut-off and herefrom detectswhether or not a proper connection is provided between a dialysissystem, especially a needle of the dialysis system, and the patientblood circulation.

Another embodiment of the invention provides an apparatus forextracorporeal blood treatment comprising a dialyser 1, a tube shut-off40, a pressure sensor 41, a data processing unit, a storage unit, whichmay be part of the data processing unit, and an output unit. Thedialyser 1 can be divided into first and second chambers 29, 30 by asemipermeable membrane, the first chamber 29 being arranged in adialysis fluid path and the second chamber 30 being connectable to theblood circulation of a patient with a blood supply line 32 and a blooddischarge line 31 of the dialyser 1. Furthermore, a bubble collector 35,38 may be provided. The tube shut-off 40 and the pressure sensor 41 arepreferably arranged in the blood discharge line 31 of the dialyser 1behind, i.e. downstream of, the bubble collector 38.

The embodiment illustrated in FIG. 1 constitutes a possible structure ofan apparatus according to aspects of the invention for extracorporealblood treatment and/or for the detection of needle dislodgement. Inanother embodiment the pressure sensor 37 can be dispensed with, forexample, as the function thereof can be assumed by the pressure sensor41 provided in this embodiment and arranged according to therepresentation in FIG. 1.

By way of the measuring data sensed by the pressure sensor 41 in theembodiment according to FIG. 1 a regular examination for venous needledislodgement is carried out. The regular examination can be a singlecheck or a multi-check. A multi-check consists of at least two singleexaminations. Likewise threefold, fourfold to n-fold examinations can becarried out during dialysis, n being a natural number larger than orequal to 5.

The examination for venous needle dislodgement is implemented in thatthe tube shut-off 40 is closed so that no more blood can flow into theblood discharge line 31 through which the blood is returned to thepatient again. Any apparatuses which inhibit the flow through the blooddischarge line 31 in the form of a tube such as tube shut-off clamps orvalves, can serve as tube shut-off 40.

When the tube 31 is disconnected, pressure measurement is then carriedout at the pressure sensor 41 continuously or at, preferably regular,time intervals until it can be determined by way of the measuredpressure values whether they tend toward atmospheric pressure.

Atmospheric pressure in this case means that the pressure toward whichthe pressure curve tends after closing the tube shut-off, does no longerinclude or reproduce the shunt or intravascular pressure, but that thesystem is open toward atmosphere via the needle connecting the blooddischarge line 31 to the patient. In this case the pressure is no longerdue to the counter-pressure in the patient access. A fluid loss occursvia the needle until the pressure inside the tubing system correspondsto the ambient pressure of the needle which is either the atmosphericpressure or the pressure in the venous patient access, each taking thehydrostatic pressure by a possible difference in height between thefluid level in the air bubble collector 38 and the venous access intoaccount.

The reaching of the different pressure levels which depends on thepressure (atmospheric pressure or patient intravascular pressure)prevailing at the outlet of the needle leading to the patient access isalso reflected by the speed at which the change of pressure takes placeafter stopping the flow by blocking the tube shut-off 40 in themeasuring device. Here the duration of the drop of pressure e.g. to36.8% of the value (1/e of the value) present with running blood flow,i.e. opened tube shut-off 40, can be used as a measure.

In addition or as an alternative, it can optionally be checked whetherafter closing the tube shut-off 40 a periodic signal can be proven whichis superimposed to the pressure signal and is generated by the pulsatingblood pressure in the patient access. If such pulsating periodic signalcannot be proven any more, this is equally indicative of venous needledislodgement, as no connection to the patient circulation system isprovided any more. If needle dislodgement is detected, preferably awarning signal is output. In one or more embodiments the tube shut-off40 in such case remains closed so that undesired discharge of the bloodinto the needle exposed to the atmosphere or undesirably leading intothe patient tissue is prevented. During the examination for venousneedle dislodgement the tube shut-off 40 remains closed.

If it is detected when checking for needle dislodgement that no needledislodgement is provided, i.e. the dialysis machine is correctlyconnected to the blood circulation of the patient, the tube shut-off 40is re-opened and the dialysis is continued until a repeated check forvenous needle dislodgement is carried out after a predetermined timeinterval. The intervals between the checks for venous needledislodgement can be automatically determined or adjustable, e.g. forhigh-risk patients tending to uncontrolled movements. In embodiments ofthe apparatus according to aspects of the invention the time intervalbetween the checks lies within the range of from 2 seconds to 5 minutesor within the range of from 10 seconds to 4 minutes or within the rangeof from 20 seconds to 3 minutes or within the range of from 25 secondsto 120 seconds, or else within the range between 30 and 60 seconds sothat a check is carried out once or twice a minute.

In one or more embodiments, the time intervals between the checks can bedetermined automatically depending on the patient's weight and the bloodflow adjusted. About 13% of the total blood volume of the patient can bewithdrawn, before an effect on the arterial pressure of the patient oron his/her cardiac output will occur. For example, in one embodimentwith the knowledge of the blood volume of the patient of e.g. 6 litersand a blood flow rate of 300 ml/min the scanning frequency can bedetermined to be 0.0083 Hz, i.e. to a measurement every 2 minutes. Theloss of blood becomes critical when 35 to 45% of the blood volume iswithdrawn. Herefrom an absolute minimum value for the scanning frequencycan be determined. Further dependent parameters can be the heart and/orrespiratory rate, accompanying diseases such as Diabetes mellitus and/orcoronary heart diseases. An adjustable individual check can be manuallycarried out or automatically triggered e.g. after an unusual unspecificpressure drop at the pressure sensor 37. If, for example, a pressuredrop of more than a reference value of e.g. 10% to 30% or more than theaverage pressure sensed by the pressure sensor 37 is determined at thepressure sensor 37, the individual check is triggered.

In embodiments of the apparatus according to aspects of the invention,as a further trigger criterion for the start of a new or additionalmeasurement the detection of a strong drop of the venous pressurebetween the measuring intervals during a current treatment can be used.This means that with continuous pressure measurement at the pressuresensor 41, when the tube shut-off 40 is opened, automatically a newmeasurement is started, when major pressure variations or a pressuredrop of e.g. more than 20% of the previously prevailing average pressureare detected during this continuous pressure measurement at the pressuresensor 41. The start of a new measurement means in this case, too, thatthe tube shut-off 40 is closed and it is measured at the pressure sensor31 whether the pressure tends toward the atmospheric pressure.

Hereinafter the operating mode of the illustrated and describedembodiment as well as a configuration of a method according to aspectsof the invention for checking and/or detecting the presence of venousneedle dislodgement will be described. By “venous needle dislodgement”also in this case a displacement including slipping out of the needleleading from the blood discharge line 31 into the patient and/orinadvertent separation or opening of the connection of the blooddischarge line 31 to the patient access, for example in the form of abayonet lock, twist lock or plug-in lock, are to be understood. Forcarrying out the check for venous needle dislodgement initially the tubeshut-off 40, for example in the form of a tube shut-off clamp, isclosed. As an alternative or in addition, the blood pump 34 can bestopped.

The pressure drop occurring at the pressure sensor 41 after closing thetube shut-off 40 is taken up at a sufficient dissolution and/or scanningrate, wherein the measuring values of the pressure drop or therespectively measured pressure established in this way are stored in theevaluation and storage unit 50. The storage unit can be an internalmemory, for instance random access memory, or else an external memory.In one or more embodiments the dissolution rate referred to as scanningrate here is within the range of from 1 to 2000 measurements per secondor within the range of from 2 to 1000 measurements per second or withinthe range of from 3 to 500 measurements per second or within the rangeof from 4 to 200 measurements per second or within the range of from 5to 100 measurements per second or within the range of from 6 to 50measurements per second. This ensures that the pressure curve isdepicted at a quality and precision sufficient for analysis.

FIG. 2 illustrates an example of the pressure curve at the pressuresensor 41 before and after needle dislodgement. The pressure at thepressure sensor 41, i.e. the pressure measured by the same, is adjustedto the level of the vascular pressure at the patient access, i.e. in theshunt, for example. Here a pressure of 25 mmHg corresponds to theaverage internal shunt pressure of an AV shunt (arteriovenous shunt)consisting of autologous material. The average internal shunt pressureof all dialysis patients with native AV shunt and AV shunts with PTFEprosthesis amounts to about 35 mmHg. A value of about 40 mmHgcorresponds to the average of 80% of all dialysis patients with nativeAV shunt. On average the internal shunt pressures of 80% of all dialysispatients with PTFE prosthesis are below 70 mmHg.

Hereinafter a pressure of 30 mmHg will be assumed by way of example.This is thus within the order of the typical pressure pulses generatedby the blood pump 34 in the current therapy.

In the embodiment according to FIG. 3 possible venous needledislodgement is detected when the blood flow is stopped. This can bedone by stopping a blood pump 34 arranged in the arterial part of theextracorporeal circulation or else by disconnecting the tubing systemwith the tube clamp 40, while the blood pump 34 is running. In anotherembodiment both the blood pump 34 and the tube clamp 40 can be jointlycontrolled so that both the active fluid delivery through the blood pump34 and the transmission of the blood through the tube clamp 40 arestopped simultaneously or else staggered in time. When the blood flow isstopped, the pressure in the entire extracorporeal blood tubing systemruns against the shunt or intravascular pressure of the patient. FIG. 3shows a typical curve progression for the pressure occurring at thepressure sensor 41 and measured by the same without venous needledislodgement, wherein the measurement is started at a time t₁ and isstopped again at a time t₂.

In the embodiment according to FIG. 4 undesired needle dislodgement orseparation of the connection between the extracorporeal circulation andthe patient access occurs at a time t₃. This needle dislodgement orseparation of the connection to the patient access is detected duringregular examination started at the time t₁ and after decrease of themeasured blood pressure below a threshold p_(Grenz) D at the time t₄results in triggering an alarm and, if necessary, additionally instopping the blood pump 34, if the latter is still running. Thethreshold p_(Grenz) can be established, for example, in that anexamination is carried out with a safely applied venous access. When thethreshold P_(Grenz) is underrun, additionally or alternatively totriggering a warning signal the dialysis process is interrupted and theapparatus for extracorporeal fluid treatment is transferred into a safestate without further withdrawal of fluid so that no damage is inflictedon the patient.

Venous needle dislodgement is detected in that pressure measuring valuesare measured at the pressure sensor 41 from the start of examination atthe time t₁ staggered in time, i.e. at time intervals, and it is checkedwhether these pressure measuring values in their drop tend towardatmospheric pressure and reach and underrun, for example, the thresholdp_(Grenz). If the pressure measuring values measured at the pressuresensor 41 show a tendency toward atmospheric pressure, i.e. a relativelyfast decrease or reaching and underrunning of the threshold p_(Grenz),the presence of venous needle dislodgement and, respectively, anundesirably faulty connection between the blood discharge tube 31 andthe patient access, e.g. the shunt, is concluded. If, however, thepressure measuring values measured at the pressure sensor 41 tend towarda typical venous pressure level and accordingly show only a smalldecrease rate and, respectively, do not reach or fall below thethreshold p_(Grenz), no venous needle dislodgement is given, and theexamination is terminated at the time t₂ (FIG. 3) and the treatment,i.e. the dialysis, is continued. This case is illustrated in FIG. 3.

Hence, with the blood pump 34 running and the tube shut-off 40 beingopened, for example, a pressure of 160 mmHg can be measured at thepressure sensor 41. If the subsequent pressure measurements at thepressure sensor 41 show a pressure drop tending toward atmosphericpressure, i.e. to a value of 0 mmHg relative to the atmosphericpressure, when the tube shut-off 40 is closed, venous needledislodgement is present and a warning is output, for example in opticalform as a visual display or in acoustic form by generating an acousticalarm, and the blood pump 34 is stopped, where necessary, unless thishas been done yet. If, however, the values of the pressure sensordetermined at the pressure sensor 41 after the start of measurement tende.g. toward 30 mmHg, this tendency value is within the range of atypical venous pressure level so that it is decided that no venousneedle dislodgement is present.

In one or more embodiments of the invention, a prediction of the curveprogression after closing the tube shut-off 40, e.g. the tube shut-offclamp, is provided so as to reduce the duration of the examination. Thiscan be done in the embodiment(s) in that by way of the first measuringvalues after the start of examination at the time t₁ a value towardwhich the pressure curve tends is extrapolated. By way of the extent ofpressure drop after closing the tube shut-off 40 a relatively reliableprediction can be made as to whether the pressure drop gradient tendstoward the venous blood pressure of the patient or toward atmosphericpressure.

Instead of or in addition to the analysis of the pressure at thepressure sensor 41 with closed tube shut-off 40, also the course of thepressure drop can be used for detecting venous needle dislodgement. Inan embodiment, e.g. the duration τ of the dying of the pressure to nomore than 36.8%, i.e. to 1/e, is used as parameter. This parameterdiffers significantly for the cases of connection and, respectively,dislodgement (FIG. 8) so that also herefrom a possible needledislodgement can be reliably detected. The control unit 50 in this casechecks the duration τ required to reach a pressure drop to 1/e oranother specified value and compares this duration τ to a time thresholdor reference value, where necessary. If the measured duration τ is belowthe time threshold, dislodgement is concluded. Otherwise the case ofproper connection is concluded and the treatment is continued. Thisapproach, too, constitutes a suitable means for detecting venous needledislodgement.

In the afore-described or other embodiments it can be alternatively oradditionally checked whether after closing the tube shut-off 40 aperiodic signal continues to be measured at the pressure sensor 41. Ifso, no dislodgement is present as the periodic signal is generated bythe pulsatile blood pressure. In this case the measurement can bedirectly interrupted and the dialysis can be continued. This course ofaction excels by the fact that the interruption of dialysis is extremelyshort. If, on the other hand, a drop of the pressure curve is obtainedwithout any modulated periodic signal, dislodgement is possible orprobable. In this case the measurement is continued in the describedembodiment until an unambiguous result is obtained. In some cases or inseveral embodiments it may also be provided to completely stop the bloodpump 34, for example when the extracorporeal storage volume provided bythe bubble collector(s) 35, 38 or other components is exhausted. In allthese cases the patient's safety is guaranteed.

Alternatively or additionally, during the examination for venous needledislodgement the blood pump 34 can continue pumping. This leads to avariation of the fill level in the venous bubble collector 38 and/or inthe arterial bubble collector 35 in which the quantity of the bloodpumped in this period is intermediately stored. FIG. 3 illustrates thatthe pressure is measured in the venous tube (line) 31 returning thepatient blood again after opening the tube shut-off 40, which results inan increase in pressure at the pressure sensor 41. Subsequent hereto thepressure falls to the basic level again, but not deeper than that. Thiscourse of action entails the advantage that no dialysis time is spoiledon checking for venous needle dislodgement, as the dialysis can becontinued during this measuring period.

For determining the final point of pressure measurement at the pressuresensor 41 a fit or a threshold or desired curve progression can beemployed. The assumed progression preferably is an exponential drop ofthe pressure according to the following formula:

F(t)=e ^((−at)) +A

wherein A is an offset value, i.e. the value toward which the functionis converging, whereas a denotes the dying constant. This is only one ofplural possible embodiments of the conversion. The behavior and/or thevariables used for the comparison can also be described by exponentialfunctions and polynomials.

The fit or, respectively, the threshold or, respectively, the referencecurve can be dynamically adapted in the course of measurement and,respectively, during the measuring period. In this embodiment new datapoints, namely, new currently established measuring values, areimmediately integrated in the fit, i.e. the desired curve or thethreshold is adapted so as to render the prediction of the final valueto be expected as precise as possible. Introducing additionalinformation in the form of new values can also influence the calculatedfinal value of the fit function or reference function, respectively.Consequently, the latter is exposed to a certain variation in thiscourse of action. This variation can be used as additional controlparameter for the reliability of the prediction of the final value. Thesmaller the variation, the more reliable and thus the more precise isthe statement. If the established variation is within an interval ofless than 20 mmHg, preferably less than 10 mmHg, or less than 5 mmHg,the measurement is judged to be completed.

By the final point of pressure measurement in this context the pressurevalue is understood which the pressure measured by the pressure sensor41 would reach according to the prediction of the fit after closing thetube shut-off 40.

The afore-described embodiments of the apparatus according to aspects ofthe invention and the method according to aspects of the invention forexamination for venous needle dislodgement excel by the fact that thevenous pressure is uncoupled from the arterial pressure in theextracorporeal circulation and there is not simply determined thedifference in pressure between the venous and arterial pressures. Thearterial pressure curve therefore is no disturbing variable, andmovements of the patient or an adjustment of the patient's lying heightor lying position do not result in a false alarm. This is due to thefact that in embodiments of the apparatus according to aspects of theinvention and the method according to aspects of the inventionexclusively a pressure drop is measured in the venous pressure behind,or downstream of, a tube shut-off and it is observed whether thepressure drop tends toward atmospheric pressure or a pressure levelcommon in the venous range. Thus a faultless and precise diagnosis canbe made.

Hereinafter a concrete embodiment will be described. At the beginning ofdialysis, first a pressure value is recorded as reference value by thepressure sensor 41 when the flow is interrupted (closing of the tubeshut-off 40) and while a properly applied venous patient access isensured. The exemplified value in this case is 35 mmHg. During the firsttreatment phase of the first two hours of treatment, for example, thetube shut-off 40 is now closed at intervals of e.g. 2 minutes and thepressure curve is recorded at the pressure sensor 41. An extrapolationof the pressure curve recorded over a particular period of e.g. 1.5 scarried out in the embodiment results in the fact that thecounter-pressure at the venous needle ranges between e.g. 30 mmHg and 40mmHg depending on the measurement. Thus the tube shut-off 40 can beimmediately re-opened so as to regularly continue the treatment of thepatient. After each measurement the intermediately stored blood volumeaccumulated in the air bubble collector 38 by the running blood pump 34with the tube shut-off 40 being closed is gradually returned into thepatient again. In order to avoid pressure peaks by opening the tubeshut-off 40 the pressure can be balanced in the air bubble collectors 38and 35. For this purpose, a pump is suited, for example, which is usedfor adjusting the fluid levels in the air bubble collectors 35, 38.

Also during this afore-described operation the blood pump 34 continuesrunning at the delivery rate selected by the user of e.g. 300 ml/min sothat, considered throughout the complete treatment, the average bloodflow corresponds to the blood pressure selected by the user.

When the treatment is continued after measurement, i.e. in the describedexample in the third hour of treatment, venous needle dislodgement nowoccurs. the subsequent measurement with closed tube shut-off 40 apressure curve which tends toward atmospheric pressure (0 mmHgdifference pressure) is detected at the pressure sensor 41. The venousneedle remains on the patient's table, for example, and is providedlevel with the pressure sensor 41. As soon as this is detected,immediately alarm is triggered and the blood treatment is interrupted,if necessary, by stopping the blood pump 34. The nursing staff now canattend to the patient and remedy the situation. After that the treatmentcan be continued.

After a particular period of e.g. 40 minutes a pressure of −70 mmHg ismeasured, for instance, whereupon the blood pump 34 is stopped and alarmis triggered. In this example, the needle has not remained on the couchbut has fallen to the ground. Thus the needle in this example isprovided below the pressure sensor 41. The hydrostatic column betweenthe pressure sensor 41 and the opening toward atmosphere (venous needleon the ground) thus generates negative pressure in the pressure sensor41.

After a further period of e.g. 20 minutes in a subsequent measurementduring extrapolation of the pressure curve from the measurement lastinge.g. 1.5 seconds, no unambiguous result is established. Simultaneouslywith the measurement, the patient has varied e.g. the position ofhis/her arm and thus caused a strong variation in the extrapolation ofthe pressure curve. At first the measurement is repeated after aspecific period of 15 seconds, for example, so as to check the result ofthe previous measurement. Since in this example again no unambiguousstatement can be made on the basis of the measuring results after e.g.1.5 seconds, the tube shut-off 40 remains closed until an unambiguousresult is provided. In such case, in addition to the bubble collector 38initially used for intermediate storage of the purified blood also thebubble collector 35 can be used as blood reservoir for still unpurifiedblood, wherein in this case the delivery volume of the dialyser 1 can berestricted or completely reduced to zero. Hence the blood volumedelivered while the blood pump 34 continues running is nowintermediately stored in the bubble collector 35. If the result still isnot sufficiently precise, the blood pump 34 in this case is equallystopped until an unambiguous result is achieved. In the describedexample, however, it is clear after a measuring time of e.g. 6 secondsthat no venous needle dislodgement is present, as the extrapolated valuenow is 35 mmHg, i.e. the value which was recorded and stored asreference value for a proper access also at the beginning of thetreatment. Hence the treatment is continued.

As afore-described, FIG. 3 shows a schematic pressure curve at thepressure sensor 41 with a correctly positioned venous needle 31 a. Theupper curve 2 a also in this case symbolizes the venous pressure curve,while the lower steady curve 2 b indicates the venous blood pressure inthe body of the patient to be subjected to the blood treatment. At a“start of examination” time t₁ the tube shut-off 40 is closed and thepressure sensor 41 measures whether a periodic signal generated by thepulsating blood pressure of the patient continues being provided and/orwhether the pressure measuring values measured by the pressure sensor 41tend toward zero.

From the curve shown in FIG. 3 it is evident that the pressure drop doesnot tend toward zero but toward approximately 80 mmHg and further aperiodic signal is continuously provided by the pulsatile bloodpressure. It is detected herefrom that no needle dislodgement ispresent, and the blood treatment is continued after the end ofexamination at the time t₂. Accordingly, the tube shut-off 40 isre-opened, wherein a pressure maximum (overshooting) may occur due tothe pressure built up ahead of (upstream of) the tube shut-off 40, as itis evident in the pressure curve progression 2 a immediately after thetime t₂.

FIG. 4 illustrates an example of a pressure curve at the pressure sensor41 of the apparatus according to aspects of the invention and the methodaccording to aspects of the invention in the case of venous needledislodgement. The upper curve 2 a also in this case symbolizes thevenous pressure curve, whereas the lower curve 2 b indicates the venousblood pressure in the body of the patient to be dialyzed. In the exampleaccording to FIG. 4, at the time t₃ needle dislodgement, i.e. separationof the connection between the blood treatment apparatus and the patientblood circulation, has occurred for example by slip-out of the venousneedle or by separation of the fluid communication established in anyway between the dialysis apparatus and the patient blood circulation.The tube shut-off 40 is closed at the time t₁ “start of examination”.Two pump strokes before the time t₁, i.e. the start of examination, atthe time t₃ in fact needle dislodgement did occur. Now the pressure inthe blood discharge line 31 tends toward atmospheric pressure afterclosing the tube shut-off 40 so that also the pressure measured at thepressure sensor 41 tends toward atmospheric pressure. The detection ofthis curve progression by the pressure measurements at the pressuresensor 41 permits the unambiguous statement that venous needledislodgement is present. For this purpose, the omission of the venouspulsations in the measured pressure signal just as the gradient of dropof the measured pressure and/or the falling of the measured pressurebelow a threshold can be evaluated and detected at a time t₄. If venousneedle dislodgement is determined, an optical, visual or other alarm canbe generated at the time t₄ and from this time also the blood pump 34can be stopped.

FIG. 5 shows an example of measurement in the case of proper needleconnection. After closing the tube shut-off 40 the course of the venouspressure measured reaches a lower minimum pressure value (p_(Grenz))measured. The threshold P_(Grenz) reached or the pressure valuecalculated from an extrapolation and corresponding to said limitp_(Grenz) can be used as a measure for the presence of needledislodgement (see FIG. 7 in this context). The value τ describes theduration of the drop in the venous pressure measured from closing thetube shut-off 40 at the time t₁ to a p_(τ) of 36.8% of its value (1/e).This value τ, too, can be used as characteristic variable fordetermining needle dislodgement (see also FIG. 8 in this context).

FIG. 6 shows the different course of the blood pressure measured duringthe examination phase in the case of connection (upper curve) anddislodgement (lower curve). These two cases can be clearly separatedfrom each other. In the case of dislodgement the measured pressuresignificantly falls below the value expected in the case of correctneedle connection.

FIG. 7 illustrates the difference between the limits or minimum valuesp_(Grenz) in the case of connection and dislodgement. It is evident thatin the range of low shunt or intravascular pressures (p_(patient)) noclear distinction can be made between connection and dislodgement. Thisfact is given, for example, when an extremely low shunt or intravascularpressure (p_(patient)) is prevailing and the venous needle afterdislodgement experiences a negative change of height. This may occur,e.g., when the needle falls down from the edge of the table. In FIG. 7the pressure values established in the case of connection includingtheir limit of variation are applied by diamonds. The measuring valuesin the event of dislodgement are shown by lying squares.

FIG. 8 shows the difference resulting in the cases of connection anddislodgement as regards the time parameter T. The case of dislodgementis illustrated here as linear approximation of the measuring valuesshown by lying squares. The case of connection, on the other hand, issymbolized as linear approximation of the diamonds. Upon evaluation thesame statements are obtained as in the case of the evaluation accordingto FIG. 7. In the extreme case the value τ can be identical forconnection and dislodgement.

The afore-described embodiments can be combined in any way, therebyseparate further embodiments being provided. In addition, the method canalso be implemented in the form of a computer program product in whichcodes for carrying out the individual method steps are included.

1-14. (canceled)
 15. An apparatus for detecting an interruption ofconnection between a blood treatment apparatus and a patient bloodcirculation which can be connected to the blood treatment apparatus viaa connection means attachable to a fluid line comprising: a lineshut-off configured to block the fluid line; a pressure sensorconfigured to measure fluid pressure in the fluid line at a positionlocated between the line shut-off and the connection means; and acontrol and evaluation unit configured to evaluate the fluid pressure orpressure curve occurring after blocking the fluid line to detect aninterruption or disturbance of the connection between the connectionmeans and the patient blood circulation.
 16. The apparatus of claim 15,wherein the apparatus is part of the blood treatment apparatus.
 17. Theapparatus of claim 15, wherein the blood treatment apparatus is adialysis apparatus.
 18. The apparatus of claim 15, further comprising atleast one of a display or an alarm device for generating a display or analarm, respectively, in the case of detection of an interruption ordisturbance of the connection.
 19. The apparatus of claim 15, whereinthe control and evaluation unit is further configured to perform atleast one of compare the fluid pressure occurring in the fluid lineafter closing the line shut-off to a threshold, determine rate ofpressure drop, determine a final pressure value to be expected, ordetect whether the fluid pressure tends toward atmospheric pressure or ahigher pressure occurring in the patient blood circulation.
 20. Theapparatus of claim 15, further comprising a blood pump which continuesto be operable even after actuation of the line shut-off withcorresponding fluid blocking of the fluid flow through the lineshut-off, wherein the pumped fluid can be intermediately stored in acollecting means.
 21. The apparatus of claim 20, wherein the collectingmeans is a bubble collector.
 22. The apparatus of claim 15, wherein thecontrol and evaluation unit is further configured to stop the operationof a blood pump when at least one of a collecting reservoir receivingthe pumped fluid is filled while the line shut-off is closed,dislodgement of the connection means is determined, or a fluid pressuremeasured by the pressure sensor reaches or underruns a specific limit.23. A method for detecting an interruption of a connection between ablood treatment apparatus and a patient blood circulation which can beconnected to the blood treatment apparatus via a connection means,comprising: measuring the fluid pressure prevailing in the fluid line atregular or irregular time intervals with a pressure sensor at a positionlocated between a line shut-off and a connection means; blocking thefluid line at regular or irregular time intervals; and evaluating thepressure or pressure curve occurring in the fluid line after blockingthe fluid line so as to detect an interruption or disturbance of theconnection between the connection means and the patient bloodcirculation.
 24. The method according to claim 23, further comprising:generating at least one of a display or an alarm in the case ofdetection of interruption or disturbance of the connection.
 25. Themethod according to claim 23, in which the pressure occurring in thefluid line after closing the line shut-off is compared to a threshold, arate of the pressure drop is determined, or a final pressure value to beexpected is determined and it is detected whether the final pressurevalue tends toward atmospheric pressure or a higher pressure occurringin the patient blood circulation.
 26. The method according to claim 23,wherein a blood pump is operated continuously even after actuation ofthe line shut-off with corresponding fluid blocking of the fluid flowthrough the line shut-off, wherein the pumped fluid is intermediatelystored in a collecting means.
 27. The method according to claim 23,wherein operation of a blood pump is terminated when a collectingreservoir receiving the pumped fluid is filled, while the line shut-offis closed.
 28. The method according to claim 23, wherein operation of ablood pump is terminated when dislodgement of the connection means isdetermined.
 29. The method according to claim 23, wherein operation of ablood pump is terminated when a fluid pressure measured by the pressuresensor reaches or underruns a specific limit.
 30. The method accordingto claim 23, wherein the line shut-off is re-opened as soon as it isdetected that no interruption or disturbance of the connection betweenthe blood treatment apparatus and the connection means is provided.